isopor

isopor [ahy-suh-pawr] Word Origin noun

1. an imaginary line on the earth’s surface connecting points of equal annual change in the declination, inclination, or other components of the earth’s magnetic field.

Origin of isopor 1930–35; iso- + -por Greek póros path, pore2 Also called isoporic line. Related formsi·so·por·ic, adjective